Multilayer armor

ABSTRACT

A multilayer armor is provided that includes a first rigid layer, a second rigid layer, and an interlayer securing the first and second rigid layers to one another. At least one of the first and second rigid layers can include a plurality of regions with a physical or material property that varies between the regions. The interlayer can have a force-extension ratio of 5,600 psi/in or less. The interlayer can have a physical or material property that varies within the interlayer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/473,559, filed on Apr. 8, 2011, the entire contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure is related to armor. More particularly, thepresent disclosure is related to multilayer armor made of materials suchas glass, glass-ceramic, or plastics, with improved multi-hitcapabilities.

2. Description of Related Art

Ballistic rounds tend to have a high aspect ratio, where the length ofthe round is several times longer than the diameter of the round, andwhere the round itself is constructed of hardened steel or tungstencarbide or the like.

It is well known to those accomplished in the art of designing,developing, manufacturing, testing ballistic armor that the armor makesa stronger and more secure defeat of the incoming round if that round iscaused to “turn” once it impacts and starts to penetrate the armor.

The key reason a turning projectile is considered so favorable todefeating the incoming projectile is that as soon as the projectile isturned it is facing a far thicker cross section of armor as the anglecreated by the turning significantly increases the distance to the backface. Stated another way, the aspect ratio of the projectile is not justvery large, where the area of the pointed tip has a dramatically smallersurface area than the surface area of the side of the projectile. Thus,turning the projectile refers to changing its angle of incidence withrespect to the armor so that more of the larger aspect ratio sidesimpact the target than the smaller aspect ratio tip.

Turning is also thought to significantly reduce the velocity and energyof the projectile since the area of the projectile interacting with thearmor translates from the cross section described by the z axis to onedescribed by it length and part of its diameter.

Additionally, the turning of incoming projectiles also changes theprofile of energy and kinetic transfer from the tip of the projectile tothe armor to the cross section described by the surface area of the sideof the projectile to the armor. In addition, it imparts torque loadsthat can bend or break the round.

In many cases the prior art armor, especially in the case of opaquearmor, has focused on construction and geometries designed to cause theturning of the incoming round. In other prior art armor, ceramic shapessuch as pyramids, balls and the like have been assembled into the strikeface or body of such armor to assure the turning of the round such asthe structures seen in U.S. Pat. Nos. 7,603,939, 7,736,474, 7,077,048,and 7,562,612.

In still other prior art armor, granular media has been used toinfluence the turning of projectiles, where the turning is effected bythe features of the granules such as size, density, packing, depth, etc.and their ability to impose lateral displacement and angular momentumsuch as the structures seen in U.S. Pat. No. 7,827,897, InternationalPublication No. WO0192810, the article by S. K. Dwividi et al., “Twodimensional mesoscale simulations of projectile penetration into drysand,” J. Appl. Phys. 104 (2008), and the article by Todd P. Broyles,“An Evaluation of the PENCURV Model for Penetration Events in ComplexTargets,” Sandia report, SAND2004-3482.

Still further, prior art armor has used the inclusion of gaps or spaceswithin the armor to encourage turning of projectiles as seen in U.S.Publication No. 20090217813 and U.S. Pat. No. 7,908,973.

Unfortunately, many of these prior art techniques for turning theprojectile cannot be applied to transparent armor as the transparencywill be diminished or eliminated by the structures describe by much ofthis prior art.

Therefore, it has been determined by the present disclosure that armor,particularly transparent glass-ceramic armor, that enhances the turningof incoming round, particularly second rounds, is a valuable way to makemore reliable and robust armor, and also a way to make the armor lessweighty.

BRIEF SUMMARY OF THE INVENTION

Armor is provided that addresses multiple hits of ballistic rounds,which tend to have a high aspect ratio, where the length of the round isseveral times longer than the diameter of the round, and where the rounditself is constructed of hardened steel or tungsten carbide or the like.

The armor of the present disclosure is configured to promote the turningof both initial and subsequent rounds or projectiles through the use ofrigid layers and/or adhesive interlayers that have varied physical ormaterial properties within that layer or interlayer.

The armor of the present disclosure provides rigid layers and/orinterlayers having non-homogeneous regions or areas therein thatinteract with an incoming projectile causing it to turn and thereby takeless thickness and weight to defeat the projectile.

The armor of the present disclosure provides rigid layers laminated byinterlayers having a force to extension ratio of 5,600 pounds per inchper inch (psi/in) or less, and preferably 2,800 psi/in at theoperational temperature of the armor, which loosely binds togetherfragments of the rigid layers impacted by a first projectile in a mannerthat promotes turning of subsequent projectiles.

A multilayer armor is provided that includes a first rigid layer, asecond rigid layer, and an interlayer securing the first and secondrigid layers to one another. In some embodiments, at least one of thefirst and second rigid layers can includes a plurality of regions with aphysical or material property that varies between the regions. In otherembodiments, the interlayer can have a force-extension ratio of 5,600psi/in or less. Further, the interlayer can have a physical or materialproperty that varies within the interlayer.

The armor of the present disclosure provides rigid layers where therigid layers are glass or glass-ceramic laminated by interlayers, wherethe strike face has a strength that is at least three times and,preferably five times, greater than a strength of the subsequent layers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 through 3 illustrate exemplary multi-hit ballistic testingpatterns;

FIGS. 4 through 18 are x-ray tomography pictures illustrating damagepatterns to glass-ceramic armor targets according to the presentdisclosure from impacts with armor piercing projectiles;

FIG. 19 is a partial perspective view of a vehicle having a windshield,a window, a headlight, or a door fabricated from an exemplary embodimentof a multi-layer armor according to the present disclosure;

FIG. 20 is a cross-sectional view of the multi-layer armor of FIG. 19taken along line 20-20;

FIG. 21 is a cross-sectional view of an exemplary embodiment of a rigidlayer having regions of variable material properties according to thepresent disclosure; and

FIG. 22 is a cross-sectional view of an exemplary embodiment of aninterlayer having regions of variable material properties according tothe present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The armor of the present disclosure relates to both opaque armor,typically used in body armor, helicopter armor, vehicle armor and thelike, and transparent armor, typically used in lights and windows invehicles, buildings, and other applications.

As used herein, the term “complete penetration” shall mean that theincoming rounds completely penetrate the armor such that spall, armor,the round itself, or pieces of the round exit the “safe” side of thearmor. The term “partial penetration” shall mean that the incomingrounds inflict damage to the armor including damage to the strike faceup to and including deformation of the back plates at the “safe side” ofthe armor.

The present disclosure is particularly related to improving themulti-hit capability of armor generally and glass-ceramic armor, inparticular. Methods of testing multi-hit capability are commonly knownas the “4 shot T” or the “4-shot rectangle” as required by the US DODTransparent Armor Purchase Description ATPD 2352; the “three shottriangle” or “four shot off-set rectangle” as required in STANAG; 38 mmto 100 mm on center shots as found in US State Department SD-STD-01.01;a 5-shot pattern from NU0108.1, where the specified number of rounds ofzero degree obliquity must be defeated in a specified geometry. Examplesof some of these testing methods are shown in FIGS. 1 through 3.

It has been determined by the present disclosure that, in prior artlaminated armor, there is less turning of a first incoming projectile orround than in subsequent projectiles or rounds. Stated another way, ithas been determined by the present disclosure that, when dealing withprior art laminated armor, subsequent projectiles or rounds experiencegreater turning than initial incoming rounds. Without wishing to bebound by any particular theory, this property is believed by the presentdisclosure to be caused by the damage to the armor incurred by theimpact of the first projectile or round. For instance, in the case ofthe four shot T, it has been determined that the second and fourthrounds are almost always turned whereas the first and third rounds areseldom turned.

Advantageously, the present disclosure provides a multi-layer armor 10,shown in FIGS. 19 and 20, that is configured to optimize the ability ofdamaged armor to turn subsequent projectiles and, in preferredembodiments, to turn the first strike too.

FIG. 19 illustrates multi-layer armor 10 in use with a vehicle 12. Here,armor 10 can be a transparent armor used in one or more locations suchas, but not limited to, a windshield 14, a window 16, and a headlight18. Further, armor 10 can be an opaque or non-transparent, which is usedin one or more locations such as, but not limited to, a door panel 22.

It should be recognized that armor 10 is illustrated by way of exampleonly in use with an automobile or truck. Of course, it is contemplatedby the present disclosure for armor 10 to find use with any vehicle suchas, but not limited to, a car, a boat, a plane, a train, a bus, andothers, and to find use with any other object such as, but not limitedto, a building window or door or wall, body armor, and others.

While the application of FIG. 19 illustrates armor 10 in a substantiallyplanar shape, it will be understood by one skilled in the art that thearmor 10 can have any desired planar or non-planar shape.

Turning now to FIG. 20, armor 10 is illustrated with reference to anincoming projectile 24 traveling along a line of flight. Armor 10includes a plurality of rigid layers 26 bonded or adhered to one anotherby interlayers 28. Armor 10 is arranged so that one of the rigid layers26, known as a strike face 30, faces the incoming projectile 24, whileanother one of the rigid layers 26, known as a backing plate or spalllayer 32 faces a safe side of the armor.

Rigid layers 26 are unitary or integral, one piece layers that can bemade of materials such as, but not limited to, glass, ceramics,glass-ceramics, and plastics. The glass and glass-ceramics can includeborosilicate, soda lime silicate, alumino silicate, lithium aluminosilicate, and any combinations thereof. Without limiting the scope ofthe present disclosure, suitable glass ceramic materials include thosehaving a crystalline phase of Beta-quartz, spinel, Beta-willemite,forsterite, spinel solid solution, mullite, and similar glass ceramicsknown in the art.

The plastics suitable for use as rigid layer 26 can include a materialsuch as, but not limited to, transparent polymers such as polycarbonate,polymethyl methacrylate (PMMA), polyurethane, nylon, polyamids, andpolyimides, with or without fiber reinforcement. Polymethyl methacrylate(PMMA), or poly (methyl 2-methylpropenoate), is the polymer of methylmethacrylate. The thermoplastic and transparent plastic is sold by thetrade names PLEXIGLASS®, PLEXIGLAS-G®, R-CAST®, PERSPEX®, PLAZCRYL®, LIMACRYL®, ACRYLEX®, ACRYLITE®, ACRYLPLAST®, ALTUGLAS®, POLYCAST® andLUCITE®. It is often also commonly called acrylic glass or simplyacrylic. Polycarbonate is sold by the trade names LEXAN® from GeneralElectric, CALIBRE® from Dow Chemicals, MAKROLON® from Bayer and PANLITE®from Teijin Chemical Limited. A suitable transparent polyurethane issold by BAE systems under the trade name CrystalGuard®. Transparentpolyamides are sold by Evonik under the trade name Trogomide®. Thesetransparent polymers may be microcrystalline where the crystallites areso small light passes through, such as Trogomide CX.

Additionally, in opaque applications, armor 10 can also include one ormore opaque layers that can form the strike face, the backing plate, orany layer therebetween. These opaque layers can be made of any desiredmaterial such as, but not limited to, steel, aluminum, titanium, and anyalloys thereof, and fiber reinforced composites for example where thefibers are high strength E-glass, S-glass, or R-glass, or aramids orultra high mollecular weight polyethelyne (UHMWPE) or polypropylenereinforcing a polymer matrix being pvb toughened phenolic, or epoxy, ora thermoplastic polyurethane or natural or synthetic rubber. Trade namesof light weight fiber reinfroced composites include aramids like Kevlarand Twaron, and UHMWPE such as Dyneema or Spectra.

Turning now to FIGS. 4 through 18, it has also been determined by thepresent disclosure that damage patterns created in multi-layer armor 10follows very repeatable patterns, this is particularly true when dealingwith rigid layers 26 that are formed of glass, ceramic, andglass-ceramic layers.

FIGS. 4 through 18 illustrate x-ray tomography, in which armor 10includes five layer glass-ceramic rigid layers 26, bonded with polymerinterlayers 28, were tested using one or more armor piercing projectiles24. Here, the detailed X-ray computed tomography shows .30 caliber armorpiercing rounds 24 in single and multiple shots at armor 10 havingglass-ceramic rigid layers 26.

The damage patterns in FIGS. 4 through 8 illustrate the damage patternin each layer of the multilayer glass-ceramic armor 10 after impact by asingle armor piercing projectile 24. The damage patterns in FIGS. 9through 18 illustrate the damage pattern in each layer of the multilayerglass-ceramic armor 10 after impact by more than one armor piercingprojectile 24, impacting at various distances from the first shot.

As shown via comparison of the Figures, the amount of damage variesgreatly through the thickness of the rigid layers 26 depending onwhether the armor 10 was impacted by one or two projectiles 24.

In the center rigid layer 26, the lateral extent of damage is onlydirectly around the projectile 24 approximately 13 millimeters indiameter. In layers 4 and 5, the damage extends laterally, a result ofthe polymer interlayer 28 pulling the glass-ceramic. Additionally, theturning of the second projectile, as compared to the first projectile 24is also shown by comparison of FIGS. 4 through 8 to FIGS. 9 through 18.

Shown is one damage pattern in FIGS. 4 through 8 with a single impact, aconcodial fracture pattern, which begins in the area of the strike pointand radiates outward. Normally, the area of glass or glass-ceramic layer26 immediately under the strike point impact is turned to powder andtends to leave a void after the impact.

Also shown is a second damage pattern in FIGS. 4 through 8 with a singleimpact, a radial crack, which starts near the origin and radiates outsomewhat uniformly and spreads out towards the perimeter of the layer26, growing less and less dense with distance from the strike point.

It has been determined by the present disclosure that the ability ofmulti-layer armor 10 to inducing the turning of subsequent rounds can begreatly influenced by ensuring that the aforementioned repeatable damagepatterns are utilized to present conditions to subsequent rounds thatinduce turning.

For example, it is believed by the present disclosure that the use ofpolymer interlayers 28 between layers 26, such as glass-ceramic layers,can be used to bond the layers to one another. These interlayers 28 canbe configured to hold the rubble formed by the first shot together sothat subsequent projectiles are induced to turn when impacting thisrubble. The binding force of interlayer 28 is a function of its elasticmodulus and thickness such that for a uniform thickness of theinterlayer, in the linear elastic regime, the force-extension ratio ofthe thickness to the elastic modulus is proportional to the strain orextension caused by a unit force. The force-extension ratio is usedherein to describe the binding force of interlayer 28 and has a unit ofmeasure of pounds per inch per inch (psi/in).

In prior art armor, the interlayers that have been used have been verystiff with high binding forces, providing a force-extension ratio ofabout 20,000 psi/in. It has been surprisingly determined by the presentdisclosure that, in these prior art systems, the fragmented glass formedby the impact of the first projectile are generally held tightlytogether by the interlayer such that the trajectory of the second shotsis only minimally and/or unpredictably affected by the fragmented glass.

Advantageously, armor 10 is configured with interlayer 28 that is muchmore compliant than previously thought possible, providing aforce-extension ratio of 5,600 psi/in or less and, preferably of 2,800psi/in at the operational temperature of the armor. Without wishing tobe bound by any particular theory, it is believed that the morecompliant interlayer 28 of the present disclosure allows the fragmentedglass to offer consistently lower resistance to subsequent incomingprojectiles, which is believed to encourage the projectile to turn in apredictable fashion.

Further, it is believed by the present disclosure that controlling theproperties of layers 26 and the interlayers 28 from one spot to another,the character of the fragment clumps or agglomerates can be managed andvaried to make the projectile 24 turn.

For purposes of clarity, the term Z axis is used herein to describe theline of fight of the projectile 24 as it approaches an armor target at 0degrees obliquity, or orthogonal to the planes of the parallel platesand polymers (i.e., layers 26 and interlayers 28) from which the armor10 is constructed. Similarly, the terms X axis and Y axis describe theplane of the plates orthogonal to the z axis describing the 0 degreeobliquity line of flight of the projectile till it impacts the strikeface.

Particularly for transparent uses, armor 10 creates variability in thecross section of the planes in the x and y axis by creating patterns ofnon-uniform properties in the glass or glass-ceramic layers 26 bychemical or thermal tempering of the plates in patterns which willcreate variability in the physical, mechanical and strength propertiesof the layers 26.

In the case of glass-ceramics layers 26, these regions may also beintroduced by extruding from multiple melt baths each containing adifferent composition and fusing the regions together during rolling.

Referring to FIG. 21, an exemplary embodiment of layer 26 is shownhaving multiple regions 34, 36, and 38 of varying physical properties.

In some embodiments, the multiple regions 34, 36, and 38 can be formedby providing one or more patterns 40 formed in or on the surface oflayer 26. Armor 10 is assembled so that patterns 40 are offset from oneanother on subsequent layers such that the condition of the layer 26 theprojectile 24 is likely to encounter in a target constructed of multipleplates will be variable plate to plate. Pattern 40 can have any desiredgeometry or design such as circles, triangles, squares, rectangles,lines, squiggles, dots, and any combinations thereof are contemplated.

Pattern 40 can be formed in layer 26 in any desired manner such as, butnot limited to, chemical etching or physical etching or via rollingduring formation of the layer. Pattern 40 can also be formed on thesurface of layer 26 in any desired manner such as, but not limited to,printing or rolling a material onto the surface of layer. When formed inlayer 26, pattern 40 can have variable depth. Similarly, when formed onthe surface of layer 26, pattern 40 can be formed with variable height.When bonding the layers 26 and interlayers 28 to form armor 10, theinterlayer can flow into and fill pattern 40.

In some embodiments, one or more of layers 26 can be formed of rigidpolymer. In these embodiments, the rigid polymer layer 26 can have withregions of varying properties using pattern 40. For instance, when layer26 is a polycarbonate or PMMA plate, the layer can include pattern 40that is can be machined or etched on its surface to provide cavities ofvarying depth and/or width, or can be punched or drilled with holes ofvarying diameter. Pattern 40 is then filled with a second material thathas an index of refraction substantially equal to that of layer 26.Preferably, pattern 40 is oriented at 8 degrees or more from any viewingangle to avoid internal reflections blocking visibility. The secondmaterial within pattern 40 can be harder than or softer than theremaining portions of layer 26.

In other embodiments, each layer 26 can be tempered to different degreesin a desired pattern within the layer to form areas 34, 36, 38 discussedabove. Additionally, each layer 26 within armor 10 can be tempered todifferent degrees plate by plate to provide differing materialproperties along the z axis.

In the case of chemical tempering, the areas 34, 36, 38 can be createdby screen printing, transfer printing or similar means of applying thepattern mask for chemical tempering.

For example, it is contemplated for layer 26 to be tempered so thatareas 34, 36, 38 of varying temper form strips 42 as shown in FIG. 21.During assembly, layers 26 are stacked on one another so that the strips42 in the various layers are angled with respect to one another.

In the case of thermal tempering, the tempering can also be performed tovarious degrees in alternating patterns through the stack, such thateach layer will offer a variable resistance to the incoming round,creating a bias in the flight to bring it to a turning motion from the zaxis.

In some embodiments, layer 26 can be formed with areas 34, 36, 38 ofdissimilar material properties by forming various shaped materials intothe layer. For example, layer 26 can be formed from a glass-ceramicsphere, which is then pressed into a flat sheet of low Tg glassymaterial. With matching refractive indexes, such a construction wouldremain transparent, while having significant material variability withinthe armor 10.

Thus, armor 10 can be configured using layers 26 that have varyingphysical properties within the layer, between the different layers, andany combinations thereof in a manner that promotes the turning of theprojectile 24.

Armor 10 can also use interlayers 28 of varying physical properties in amanner that promotes the turning of the projectile 24. For example,interlayer 28 can have varying physical properties within theinterlayer, between the different interlayers, and any combinationsthereof. The interlayer 28 can be transparent or opaque and can beformed of any desired transparent adhesive such as, but not limited toaliphatic polyether polyurethanes or poly(vinyl butyral)s,ethylene/methacrylic acid copolymer, silicone, epoxy, and anycombinations thereof.

Other suitable transparent polymer interlayers 28 include transparentthermoplastics or thermosets such as acrylonitrile-butadiene-styrene(ABS), acetal resins, cellulose acetate, cellulose acetate butyrate,cellulose acetate propionate, cellulose tri-acetate, acrylics andmodified acrylics, allyl resins, chlorinated polyethers, ethylcellulose, epoxy, fluoroplastics, ionomers (like Dupont Surlyn A),melamines, nylons, parylene polymers, transparent phenolics, phenoxyresins, polybutylene, polycarbonates, polyesters, polyethylenes,polyphenylenes, polypropylenes, polystyrenes, polyurethanes,polysolphones, polyvinyl-acetate, polyvinyl butyral, silicones, as wellas styrene-acrylonitride and styrene-butadiene copolymers.

It has been determined by the present disclosure that varying propertiesin the interlayers 28 can also affect the distribution of fragmentsformed by the first strike. As discussed above, regions of theinterlayer 28 with higher stiffness will clamp the fragments moretightly together than regions with lower stiffness.

An exemplary interlayer 28, having regions 44 of variable properties, isshown in FIG. 22. Interlayer 28 is can be formed by using for example,side-by-side co-extrusion to form regions 44 of varying properties.Interlayer 28 formed in this manner can be used as a single ply, or inlaminate of multiple plys with each ply being laid on top of one anotherso that the regions 44 of the laminate are have angular orientationswith respect to one another such as 0/90 degree, 0/45/45, 0/60/60 etc.

Of course, it is contemplated by the present disclosure for interlayer28 to have discrete regions 44 such as squares, circles, triangles, etc.that can be made by point-by-point extrusion into a sheet ofthermoplastic or thermal set adhesive.

Experimental Results

Three samples of target armor 10 were made and tested against the .30caliber AP M2 at an impact velocity of 2850 feet per second (fps). Thethree samples of target armor 1—were designed to allow the projectile topenetrate. All three samples were constructed having eight layers 26 andsix interlayers 28 and were bonded using a known vacuum bag andautoclave process.

The construction of the layers and interlayers of each of the threeseries of targets is seen in Table 1.

Sample #1 Sample #2 Sample #3 Layer 1 6.5 millimeters (mm) of — —borosilicate glass Interlayer 0.1 inches of — 0.1 inches TPU havingside- thermoplastic by-side discontinuities polyurethane (TPU) Layer 20.125 inches of 0.125 inches of perforated — polycarbonate and urethanefilled polycarbonate Interlayer 0.1 inches of TPU — 0.1 inches TPUhaving side- by-side discontinuities Layer 3 6.5 mm of borosilicate — —glass Interlayer 0.1 inches of TPU — 0.1 inches TPU having side- by-sidediscontinuities Layer 4 9 mm of borosilicate glass — — Interlayer 0.1inches of TPU — 0.1 inches TPU having side- by-side discontinuitiesLayer 5 6.5 mm of borofloat — — Interlayer 0.1 inches of TPU — 0.1inches TPU having side- by-side discontinuities Layer 6 0.125 inches0.125 inches of perforated — polycarbonate and urethane filledpolycarbonate Interlayer 0.1 inches of TPU — 0.1 inches TPU having side-by-side discontinuities Layer 7 0.125 inches 0.125 inches of perforated— polycarbonate and urethane filled polycarbonate Interlayer 0.1 inchesTPU — 0.1 inches TPU having side- by-side discontinuities Layer 8 0.063inches of — — polycarbonate

In the second sample, the three layers 26 of 0.125 inch polycarbonatefrom the first sample were replaced with layers 26 having pattern 40perforated therethrough and filled with a transparent urethane having adensity 10% less than polycarbonate and having a shore A hardness of 95whereas polycarbonate is much harder at Rockwell M70. The urethanefiller has a tensile strength of 28 MPa whereas the unperforatedpolycarbonate layer has a tensile strength of 55-75 MPa.

In the third sample, the 0.1 inch TPU interlayers layers from the firstsample were replaced with interlayers having side-by-side propertydiscontinuities on the order of 0.3″ scale where one TPU had a Shore Ahardness of 70 and the other a shore A hardness of 95 and an attendantdifference in elastic modulus. Densities of the side-by-side areas weresimilar.

The track of the projectile exiting each of the three samples wasdetermined by determining an angle of obliquity with which theprojectile exiting the sample would impact a residual block. After theprojectile was allowed to pass through the sample, a transparentresidual block of polycarbonate was positioned one and a half inchesbehind the back of the test target. Then, a probe was inserted into thetest target and aligned with the path through the tested sample.Finally, the angle that the probe made with the face of thepolycarbonate residual block was measured using a protractor.

Each sample was impacted two times; the first shot was placed in thecenter of the sample and the second shot was placed into a damage regionwhere the first layer of glass was still full thickness but the glasswas badly cracked with radial, circumferential and transverse cracksmaking it opaque. The placement of the second shot was varied between42.5 mm and 50.5 mm away from the first shot.

The results are shown in Table 2.

Target AD Target Shot 1 exit Shot 2 exit Sample (psf) Thickness (in)obliquity (deg) obliquity (deg) 1 19.4 2.25 0-3 30-43 2 19.5 2.27 2-843-50 3 19.3 2.20 15-30 50-58

It can be seen from Table 1 that the interlayers 28 in all three of thesample targets were all 0.1″ thick, providing the desiredforce-extension ratio of 2,800 psi/in. Further, it can be seen fromTable 2 that 100% the second shots turned with significant andrelatively consistent exit obliquities.

The results presented in Table 2 also show an increase in the obliquityof the projectile of the second shot for both cases of side-by-sidediscontinuities (samples 2 and 3) as compared to sample 1, which lacksthe side-by-side discontinuity. The effect on the first shot issurprisingly effective with the discontinuity in the interlayer 28,showing the importance of the interaction with the glass in turning afirst shot; indicating that side-by-side discontinuities in the glasslayers would also provide noticeable turning of the first shotprojectile.

In some of the examples discussed above, the side-by-side discontinuityis in the layer 26 and/or interlayer 28, namely in the plane defined bythe x and y axes. In some embodiments of the present disclosure, armor10 is configured to provide discontinuity between material propertiesalong the direction of flight.

For example, it is contemplated by the present disclosure for strikeface 30 and/or one or more layers 26 proximate to the strike face tohave a strength that is 3 or more times higher than the strength of theremaining layers 26. In some embodiments, strike face 30 and layer 26immediately adjacent to the strike face are 3 or more times stronger,and preferably 5 or more times stronger, than the layers 26 in the restof armor 10.

As used herein, the term “strength” means resistance to failure inflexural bending and especially bi-axial bending such as induced by ringon ring testing where the results are less sensitive to edge effects ascompared to modulus of rupture values based on three or four pointbending.

Nine samples of target armor 10 were made with the strike face layer 30and the layer 26 immediately adjacent thereto made of high strengthglass having a characteristic strength approximately 5 times greaterthan the sublevel glass-ceramic layers 26 and approximately 8 timesstronger than the sublevel plastic layers 26. In the multi-hit shots allof the projectiles stopped approximately 64% of the way through thetarget whereas in prior art armor of a similar number of layers 26 andinterlayers 28 having with the first and second layer of the samestrength as the sub-level layers, 33% of the multi-hit shots penetratedthrough 79% or more of the target thickness to the point where theycould be seen through the transparent polycarbonate on the safe side.

An added advantage, armor 10 having high strength strike face 30 alsoprovide increased resistance to scratching or chipping from smallobjects that may impact the transparent armor in use, or get draggedover the windows during use.

While the present disclosure has been described with reference to one ormore exemplary embodiments, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of thepresent disclosure. In addition, many modifications may be made to adapta particular situation or material to the teachings of the disclosurewithout departing from the scope thereof. Therefore, it is intended thatthe present disclosure not be limited to the particular embodiment(s)disclosed as the best mode contemplated, but that the disclosure willinclude all embodiments falling within the scope of the presentdisclosure.

What is claimed is:
 1. A multilayer armor comprising: a first rigidlayer; a second rigid layer; and an interlayer securing the first andsecond rigid layers to one another, wherein at least one of the firstand second rigid layers is divided into strips having varying degrees oftempering.
 2. The multilayer armor of claim 1, wherein the first andsecond rigid layers and the interlayer are each transparent and havematching refractive indicies such that the armor is transparent.
 3. Themultilayer armor of claim 1, wherein each of the first and second rigidlayers comprises a physical or material property that varies within thelayer.
 4. The multilayer armor of claim 1, wherein the first and secondrigid layers are made of a material selected from the group consistingof glass, ceramic, glass-ceramic, and plastic.
 5. The multilayer armorof claim 1, wherein said tempering is chemical or thermal tempering. 6.The multilayer armor of claim 1, wherein each of the first and secondrigid layers is divided into strips having varying degrees of tempering,and the strips in the first rigid layer and the strips in the secondrigid layer are angled with respect to one another.
 7. The multilayerarmor of claim 1, wherein the at least one of the first and second rigidlayers is a rigid polymer layer having cavities defined therein, and therigid polymer layer includes a different material within the cavities,wherein the different material has an index of refraction substantiallyequal to that of the rigid polymer layer.
 8. The multilayer armor ofclaim 1, wherein the at least one of the first and second rigid layerscomprises a glass-ceramic sphere that is flattened.
 9. The multilayerarmor of claim 1, wherein said first rigid layer is a glass orglass-ceramic layer comprising a strike face, wherein the strike facehas a strength that is at least three times greater than the strength ofthe second rigid layer.
 10. The multilayer armor of claim 1, whereinsaid interlayer has a physical or material property that varies withinthe interlayer.
 11. The multilayer armor of claim 1, wherein saidinterlayer has a force-extension ratio of 5,600 psi/in or less.